The present invention pertains generally to disk-type mechanical filters and specifically to a means for efficaciously attaching the ferrite transducer rod of the filter to a disk resonator.
Disk-type mechanical filters, such as disclosed in U.S. Pat. No. 3,633,133 entitled "Narrow Bandwidth Mechanical Filter Using Large Area Coupling Wires," may employ ferrite transducer rods to magnetostrictively convert between electrical and mechanical energy. The transducer is normally attached to the center of a disk resonator which comprises the filter, by bonding with a special adhesive; curable epoxy being commonly used (ferrite materials not being suitable for welding). The simple technique of using the proper bonding adhesive to attach the transducer to the disk eliminates what would otherwise be an extremely difficult mechanical attachment problem. Although this bond provides an efficacious attachment to the disk, it has been found that high humidity conditions reduce the bonding strength of the adhesive sufficiently so that under the vibrational stresses to which they are subjected, the ferrite transducers tend to become detached from their disks. Although there are epoxies that exhibit good bonding strengths even at high humidity, their moduli of elasticity vary too erratically with changing temperature conditions to achieve a necessary constant coupling coefficient between the transducer and disk to assure uniform operating filter characteristics over the temperature range to which the filter may be exposed. Thus, these high moisture resistant epoxies are unsuitable for use in attaching the transducers to the disks. Although the problem could be obviated by housing the filters in hermetically sealed cases so as to insulate them from humidity, such a solution is not commercially acceptable because of the associated high cost which would render the filter economically noncompetitive.
With the foregoing in mind, it is a primary object of the present invention to provide a new and improved means for attaching ferrite transducer rods to disk resonators such as used in mechanical filters.
It is a further object of the present invention to provide such a new and improved means of attachment which even under high humidity conditions, is efficacious, yet is inexpensive and avoids mechanical means which are impractically difficult to use.
The foregoing objects, as well as others, and the means by which they are achieved through the present invention, may best be appreciated by referring to the Detailed Description of the Invention which follows hereinafter together with the appended drawing.